Project Summary/Abstract Harnessing our immune system to fight HIV presents tantalizing possibilities. An effective vaccine could prevent the ~2 million new infections that continue to occur each year, and immune targeting of latently- infected cells could significantly advance cure strategies. However, the traditional approaches based on eliciting adaptive B and T cell responses have typically led to narrow immune responses that are not effective against the vast diversity of HIV strains circulating worldwide. The challenge is more acute for individuals infected through injection drug use, as current vaccine efforts are exclusively focused on sexually-transmitted HIV strains, which typically establish infection with only a single strain and must pass through an epithelial barrier to establish infection. In contrast, individuals who are infected with HIV through injection drug use are more likely to be infected with multiple strains with different antigenic properties. We propose pioneering a novel approach to improve immune targeting of HIV by harnessing natural killer (NK) cells, with a particular emphasis on the unique strains transmitted through injection drug use. We have exciting new data indicating that NK cells have a surprising degree of specificity in their antiviral responses. The communication between the NK cell and an infected can control the quality and the quantity of the immune response, affecting the balance between killing of infected cells and secreting cytokines that can enhance or dampen the immune response. In order to define the mechanisms that control the quality of the NK cell responses to HIV, we propose identifying the viral components that drive NK cell activation and escape, and how these components differ in HIV strains transmitted through injection drug use. Using advanced single- cell techniques, we will also define the precise NK cell subsets and activation pathways required to generate an effective NK cell response and how control of these pathways is maintained at the epigenetic level. Together, these approaches will identify the viral and cellular components required for specific innate targeting of HIV, allowing us to make informed choices in the development of vaccines and therapeutics to elicit NK cell responses that promote viral eradication.